The invention is based on a method for measuring or monitoring a mechanical motion of a magnet valve armature of electrically controlled injection systems, as defined hereinafter.
In one such known method of this kind (German Offenlegungsschrift 37 30 523), to monitor the mechanical motion of a magnet valve armature, the change in induction in the secondary coil, particularly that resulting from turning off the electric current in the magnet coil, is measured and further processed in a monitoring unit. Until the actual onset of motion of the armature in the direction resulting from the restoring force, there is a delay in the microsecond range, which can be extrapolated to determine the actual value of the adjustment, because it repeats with adequate precision in the various switching events.
Especially in fuel injection systems in which the valve closing member and the magnet armature are connected to one another and in which the injection process occurs while the magnet valve is closed, for instance so that, the closure or opening of the magnet valve determines the onset or end of injection, it is important that this opening or closing time be adhered to very precisely. The known method can ascertain only the instant of closing with high accuracy, because as a result of the applied voltage and its current imposition, accurate induction values of the magnet coil through the secondary coil can be ascertained for the closing process. When the current is turned off, the corresponding inductance signal does not immediately match the return stroke motion of the armature or in other words the onset of opening of the valve, even though the armature and the movable valve member are joined together in a manner fixed against relative motion, because a number of influences, especially hydraulic ones, are present that cannot be extrapolated computationally via the control unit and become an error in determining the quality of the injection.